Hopper23 :
PyjamasCat :
What is your budget?
(Found this: http://pcpartpicker.com/part/gskill-memory-f31600c9d16gxm)
Anything under $120.
The Cheapest 2x 8GB RAM I could find. 1600MHz CL11 (Probs 11 11 11 38 or something like that, as the website does not detail this.)
Do you need performance RAM? It might be best to save a little if you want something which is faster or more likely to clock faster.